In basic acid–base terminology, what pH range correctly characterizes an alkaline (basic) aqueous solution at 25°C?

Introduction / Context:
Understanding how pH reflects the acidity or basicity of water based solutions is fundamental in chemistry, environmental engineering, and bioprocess control. pH is a logarithmic measure of hydrogen ion activity. At 25°C, a neutral solution has pH 7, acidic solutions are below 7, and alkaline (basic) solutions are above 7. This question checks whether you can correctly map qualitative terms like alkaline to their quantitative pH interval.

Given Data / Assumptions:

• Temperature reference is 25°C, where water autoionization constant Kw is 1.0 * 10^-14.
• Neutral water has pH = 7.00 at 25°C.
• Alkalinity corresponds to excess hydroxide relative to hydrogen ions.

Concept / Approach:
By definition, pH = -log10[H+]. When [H+] equals 1.0 * 10^-7 mol L^-1, pH is 7 (neutral). If [H+] decreases below 10^-7, the pH increases above 7. Such solutions contain a higher proportion of hydroxide ions than hydrogen ions and are called alkaline or basic. Conversely, if [H+] increases above 10^-7, pH falls below 7 and the solution is acidic. These thresholds are standard at 25°C and are widely used in analytical and industrial practice.

Step-by-Step Solution:
Identify the neutral reference: pH = 7 at 25°C.Define acidic vs basic: acidic if pH < 7, basic if pH > 7.Match term alkaline with pH > 7.Select the choice that states pH > 7.

Verification / Alternative check:
Because pOH = 14 - pH at 25°C, an alkaline solution has pOH < 7, confirming that [OH-] > [H+], which is equivalent to pH > 7.

Why Other Options Are Wrong:
7: Identifies neutrality, not alkalinity.< 7: This is the acidic region.Constant over a wide range: pH varies with composition; no wide constant region defines alkalinity.

Common Pitfalls:
Confusing neutrality with alkalinity; ignoring temperature dependence of Kw outside 25°C; assuming logarithmic scale changes are linear in concentration space.

Final Answer:
> 7